1. Field of the Invention
The present invention relates generally to the field of fluid delivery systems and more are specifically, to a regulator bag for an ink delivery system.
2. Description of Related Art
Inkjet technology is relatively well developed. The basics of this technology are described by W. J. Lloyd and H. T. Taub in xe2x80x9cInkjet Devices,xe2x80x9d Chapter 13 on Output Hardcopy Devices (Ed. R. C. Durbeck and S. Sherr, Academic Press, San Diego, 1988) and in various articles in the Hewlett-Packard Journal, Vol. 36, No. 5 (May 1985), Vol. 39, No. 4 (August 1988), Vol. 39, No. 5 (October 1988), Vol. 43, No. 4, August 1992), Vol. 43, No. 6 (December 1992) and Vol. 45, No. 1 (February 1994).
The typical thermal inkjet print head has an array of precisely formed nozzles attached to a print head substrate that incorporates an array of firing chambers that receive liquid ink (i.e., colorants dissolved or dispersed in a solvent) from an ink reservoir. In what is sometimes referred to as a disposable print cartridge, the ink reservoir is an integral element with the print head, sometimes referred to as on-axis.
Alternatively, the pen can be a free-ink type print mechanism, where the ink is supplied to the print head mechanism from a separate, self-contained ink supply such as a biased ink bladder or bag (see U.S. Pat. No. 5,359,353, Hunt et al., assigned to the common assignee of the present application) sometimes referred to in the art as off-axis. An on-axis regulator mechanism is provided with the pen to control ink flow and print head pressure; one such regulator mechanism is disclosed by S. Dana Seccombe et al. in U.S. Pat. No. 5,650,811 for an Apparatus for Providing Ink to a Printhead (assigned to the assignee of the present application).
Each firing chamber has a thin-film resistor, known as a firing resistor or heater resistor, located opposite the nozzle such that ink can collect between the heater resistor and the nozzle. When electric printing pulses heat the print head firing resistor, a small portion of the ink near it vaporizes and ejects a drop of ink from the print head via a nozzle orifice. The nozzles are arranged in a matrix array. Properly sequencing the operation of each firing resistor causes alphanumeric characters or graphics images to form on paper as the print head is scanned across adjacently positioned print media and a dot matrix of ink drops is printed to form a graphics image and alphanumeric characters.
In an effort to reduce the cost and size of inkjet printers and to reduce the cost per printed page, engineers have developed inkjet printers having small, moving print heads that are connected to large stationary ink reservoirs by flexible ink tubes. This development is called xe2x80x9coff-axisxe2x80x9d printing. In such printers the mass of the print head is greatly reduced so that the cost of the print head drive system and the overall size of the printer can be minimized. In addition, separating the ink reservoir from the print head allows the ink to be replaced as it is consumed without requiring frequent replacement of the costly print heads.
With the development of off-axis printing has come the need for numerous flow restrictions to the ink between the ink reservoir and the print head. These restrictions include additional orifices, or ink ports, narrow conduits, and shut-off valves. To overcome these flow restrictions and also to provide ink drops reliably over a range of printing speeds, ink is now transported to the print head at an elevated pressure and a pressure reducer is added to deliver the ink to the print head at an optimum back pressure (an internal negative pressure gauged at the print head that is substantially less than the pressure at the ink reservoir and through the conduits).
One difficulty in the evolution of off-axis printing is the increasing need to maintain the back pressure of the ink at the print head to within as small a range as possible. Changes in back pressure greatly affect print density and print quality, and major changes in back pressure can cause either the ink to drool out of the nozzles or the print cartridge to deprime.
There are several causes for such changes in back pressure. One cause occurs when air (including both ambient air and gasses out gassed from the ink) is entrapped within the print cartridge and the print cartridge is subjected to changes in environmental parameters such as altitude and temperature. Back-pressure will be affected by changes in either the ambient atmospheric or the internal pressure conditions. Temperature variations may cause the ink and air within the ink-jet pen to contract or expand, affecting the back-pressure. Another cause of changes in back pressure is the delay between the time the print head starts to eject ink during on-demand printing and the time the pressure regulator actuates to restore the back pressure.
These complications, as well as the use of pressurized ink delivery systems, have resulted in a need for more accurate back pressure regulation at inkjet print heads and for more precise compensation techniques.
In a foam reservoir print cartridge, the capillary action of the foam will generally be sufficient to create the desired back-pressure. In a free-ink reservoir type ink-jet pen, a variable-volume, on-board, ink containment supply is often employed. For example, the reservoir may be of a biased, flexible material which can expand or contract, or an ink containment chamber may be provided which includes an internal pressure regulating device. In U.S. Pat. No. 4,509,602 (assigned to the assignee of the present invention), a spring pulls an ink-filled bladder membrane outwardly to create a slight negative pressure inside the ink reservoir. U.S. Pat. No. 4,677,447 (assigned to the assignee of the present invention) describes the use of a check valve in a printing device with an on-board ink reservoir that maintains a constant pressure difference between the ink reservoir and the ink-jet printhead. U.S. Pat. No. 4,992,802 (assigned to the assignee of the present invention) teaches the use of two pressure control mechanisms to extend the environmental operating range of an ink-jet pen. U.S. Pat. No. 5,650,811 (Seccombe et al.) for an Apparatus for Providing Ink to a printhead (assigned to the assignee of the present application) describes a diaphragm type pressure regulator located on-board an ink-jet pen using an off-board ink reservoir.
One type of back pressure regulator utilizes a regulator bag with a spring-loaded actuation lever (U.S. Pat. No. 5,975,686, Hauck, et al. Regulator for a Free-Ink Inkjet Pen, assigned to the assignee of the present application). The regulator bag may be made of multiple layers that are co-extruded (U.S. Pat. No. 6,196,669, Harvey, et al., High Durability pressure Control for Use in an Ink Delivery System, assigned to the assignee of the present application). In typical current bag designs, the shorn edges of the multi-layer-films are in direct fluidic contact with the ink. This contact can allow the ink to attack the tie layer bonding the films together. The ink attack can lead to a loss of adhesion between the tie layer and the film, causing delamination among the film layers. Failure of the regulator bag can lead to lack of backpressure resulting in unacceptable print quality, or worse.
The film based regulator bags also require thermal forming to create the requisite xe2x80x9clungxe2x80x9d geometry. The process of thermal forming stretches the bag in certain areas. This stretching can create stress the bag material, causing local changes in the film properties (such as water vapor transmission rate and oxygen transmission rate), and weakening the bag.
Another regulator design consists of a bag with an interior spring captured between the side lungs (see, for example, U.S. Pat. No. 5,440,333, Sykora et al., Collapsible Ink Reservoir with Protective Bonding Layer for the Pressure Regulator, and U.S. Pat. No. 5,450,112, Scheffelin, Laminated Film for Ink Reservoir, both assigned to the assignee of the present application). This type of regulator bag is similar in function, but uses an interior spring, rather than an exterior spring, to create forces to oppose the internal pressure. These designs required semi-complex manufacturing methods, including spring forming and second shot molding onto the pen body.
As the art of inkjet printing continues to mature, there is a continuing need for printer components that are lower in cost, easier to handle, require fewer critical tolerances, and yet provide improved reliability. Further, there is a need for assembled components that have lower part counts and are easier to assemble. Lastly, there is an ongoing need for robust fluidic seals and ink conduits for the ink delivery systems in inkjet printing systems.
Embodiments of the present invention comprise over-molded regulator bags for a fluid delivery system. The regulator bags are formed by over-molding a resilient bladder of an elastomeric material on a supporting rigid host substrate. The over-molding process allows three dimensional lung designs to be created without extra processes, and without stressing the membrane material.
Embodiments of the invention eliminate the need for an external spring to create an opposing pressure to deflate the bags when required. The inherent elasticity of the over-molded bladders act as the restoring force to return the expanded bag back to its original form.
Over-molding also allows for multiple bladders to be created in single manufacturing process, thus enabling more complex, yet cost effective, ink delivery systems.
Other aspects and advantages of the present invention will become apparent from the following detailed description, taken in conjunction with the accompanying drawings, illustrating by way of example the principles of the invention.